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Five o'clock on Friday means happy hour, the start of the weekend, and, on May 31, it meant hello asteroid 1998 QE2 - and its moon.
This has been a year for rocky visitors to our neighborhood. On Feb. 15, a small asteroid we didn't know was coming exploded in the atmosphere above Russia. Later that same day, a separate, previously discovered 150-foot asteroid (2012 DA14) came within 17,150 miles of Earth, the closest known flyby in history. On March 5, comet PanSTARRS (C/2011 L4) made its closest approach to Earth at around 100 million miles. And on Dec. 26, 2013, comet ISON will make its closest approach to us.
Our latest visitor, asteroid 1998 QE2, made its closest approach to Earth of about 3.6 million miles at 4:59 p.m. on May 31. QE2 was the size of the Golden Gate Bridge - large enough, apparently, to generate the gravity for its own orbiting moon.
NASA was excited because QE2 gave scientists the chance to snap photos from the ground of an asteroid's surface that rival those obtained when spacecraft are dispatched. Scientists also are intrigued because this 1.7-mile-wide asteroid is binary, meaning it has a moon orbiting it; QE2's moon is 2,000 feet wide.
This situation is uncommon, but not rare. NASA says an estimated 15 percent of asteroids travel in groups of two or three objects revolving around one another. What makes QE2 special is its size and proximity to Earth along its travels.
QE2 is speeding into the distance now, but scientists are still imaging the asteroid through today with two radar antennas in California and Puerto Rico. If you missed it this year, it'll be back July 12, 2028 - approaching us at a much less exciting distance of 45 million miles.
June 12: Mercury will be at its farthest angle from the sun (greatest elongation) and at its highest point in the sky after sunset. This is the best time to observe Mercury since it never climbs very high above the horizon. One neat thing you'll notice is that, since it's an inner planet, it has "phases" of light and shadow like the moon.
June 21: June solstice. Our North Pole will be tilted toward the sun, which will have reached its northernmost position in the sky. This is the first day of summer in the Northern Hemisphere and the first day of winter in the Southern Hemisphere.
June 23: Full moon. Early Native American tribes called this the Full Strawberry Moon because it signaled the time of year to gather ripening fruit. It also coincides with the peak of the strawberry harvesting season.